Abstract

The observation of latent light-assisted poling (LAP) in lithium niobate single crystals is reported. More specifically, the nucleation field is reduced and remains reduced for an extended time period (up to several hours) after irradiation with ultrafast (~150 fs) laser light at a wavelength of 400 nm. The maximum nucleation field reduction measured using latent-LAP (62%) was significantly higher in comparison with regular non-time-delayed LAP (41%) under identical irradiation conditions in undoped congruent lithium niobate crystals. No latent-LAP effect was observed in MgO-doped crystals for the experimental conditions used, despite the strong effect observed using regular LAP. The latent-LAP effect is attributed to the formation of a slowly decaying photo-induced space-charge distribution which assists local ferroelectric domain nucleation. The dynamics of latent-LAP are compared with the dynamics of photorefractive grating decay, recorded in lithium niobate crystals of different doping, confirming the space charge hypothesis.

Figures (8)

Preferentially inverted ferroelectric LLAP domains, revealed as unetched + z face after HF etching, are induced by I = 9 GW/cm2 of 400 nm fs-laser irradiation, followed by applied E-fields of (a) 14 kV/mm and (b) 8 kV/mm after a voltage delay time of 570 s in undoped CLN. LLAP domain walls run parallel to both y- and x-axes, particularly for the higher E-field in (a).

Log plot of the square root of the inverted LLAP domain area, A1/2, as a function of the voltage delay time for different laser intensities and E-fields. The solid red lines serve as a guide to the eyes.

Interferometric setup for recording and monitoring photorefractive gratings in LN using 150 fs ultrafast (UF) laser pulses at λr = 400 nm. The diffracted light (DL) of a c.w. HeNe laser at λp = 633 nm incident at the Bragg angle was used to monitor the grating recording/decay. M: mirror, BS: beam splitter, PM: optical power-meter. The period of the grating was ~1 μm. Spot diameters of the ultrafast and HeNe lasers are 1 and 0.8 mm respectively. The polarizations of both lasers were in the plane of the page (horizontal). The arrowed dash line indicates the variable arm of the interferometer.

Relative reduction of the square root of the normalized diffraction efficiency of the PR grating from 60 s to 720 s, ∆η1/2, as a function of HeNe laser intensity for undoped CLN. The solid red curve is a guide to the eyes. The range of the relative reduction of the square root of the inverted LLAP domain areas in Table 1, ∆A1/2, is indicated by the horizontal lines while the vertical lines indicate the corresponding range of HeNe laser intensities.

Tables (2)

Table 1 Summary of constants L0, time constants τL, decay rates τL−1 and the relative reductions ∆A1/2 from 60 s to 720 s of the linear dimension of the LLAP inverted domains in undoped CLN for different experimental conditions.

Metrics

Table 1

Summary of constants L0, time constants τL, decay rates τL−1 and the relative reductions ∆A1/2 from 60 s to 720 s of the linear dimension of the LLAP inverted domains in undoped CLN for different experimental conditions.

E (kV/mm)

I (GW/cm2)

L0 (µm)

τL (s)

τL-1 (× 10-4 s-1)

∆A1/2

8

4.5

42.4

2860 ± 120

3.50 ± 0.29

0.206

8

9

47.3

3970 ± 470

2.52 ± 0.61

0.153

8

18

54.8

4050 ± 250

2.47 ± 0.31

0.150

14

9

60.8

3010 ± 450

3.33 ± 1.02

0.197

10

9

47.5

2750 ± 250

3.64 ± 0.67

0.213

6

9

35.5

3150 ± 390

3.17 ± 0.80

0.189

Table 2

Summary of the decay time constants τ, stretch factors β, decay rates τ−1, and the relative reduction of the normalized PR grating diffraction efficiency ∆η1/2 from 60 s to 720 s, recorded in undoped CLN and MgO:CLN for different HeNe laser intensities Ip.

Crystal

Ip (W/cm2)

τ (s)

β

τ-1 (s-1)

∆η1/2

undoped CLN

0.71

2400

0.560

4.17 × 10-4

0.318

0.53

3040

0.581

3.29 × 10-4

0.282

0.35

4060

0.602

2.46 × 10-4

0.239

0.18

6370

0.640

1.57 × 10-4

0.179

0.088

10100

0.694

9.90 × 10-5

0.123

0.044

16600

0.734

6.01 × 10-5

0.0802

0.018

29600

0.841

3.38 × 10-5

0.0378

0.0088

81500

0.779

1.23 × 10-5

0.0213

MgO:CLN

1.0

2.27

0.282

4.41 × 10-1

0.46

3.01

0.287

3.32 × 10-1

0.13

5.29

0.312

1.89 × 10-1

0.013

15.8

0.355

6.34 × 10-2

Tables (2)

Table 1

Summary of constants L0, time constants τL, decay rates τL−1 and the relative reductions ∆A1/2 from 60 s to 720 s of the linear dimension of the LLAP inverted domains in undoped CLN for different experimental conditions.

E (kV/mm)

I (GW/cm2)

L0 (µm)

τL (s)

τL-1 (× 10-4 s-1)

∆A1/2

8

4.5

42.4

2860 ± 120

3.50 ± 0.29

0.206

8

9

47.3

3970 ± 470

2.52 ± 0.61

0.153

8

18

54.8

4050 ± 250

2.47 ± 0.31

0.150

14

9

60.8

3010 ± 450

3.33 ± 1.02

0.197

10

9

47.5

2750 ± 250

3.64 ± 0.67

0.213

6

9

35.5

3150 ± 390

3.17 ± 0.80

0.189

Table 2

Summary of the decay time constants τ, stretch factors β, decay rates τ−1, and the relative reduction of the normalized PR grating diffraction efficiency ∆η1/2 from 60 s to 720 s, recorded in undoped CLN and MgO:CLN for different HeNe laser intensities Ip.